Income Taxes - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		12 Months Ended
	Jan. 17, 2018	Dec. 29, 2018	Sep. 29, 2018	Dec. 26, 2020	Dec. 28, 2019	Dec. 29, 2018
Income Tax Contingency
TCJA one-time charge		$ 3,200
Toll charge, noncurrent				$ 20,800
Toll charge, current				3,000
Change in unrecognized tax benefits					$ 3,300
Income taxes paid				35,200	47,600	$ 46,200
Income tax refunds				7,600	7,100	4,300
Unremitted earnings of the Company’s non-U.S. subsidiaries				767,000
Deferred tax liabilities recognized on foreign earnings				$ 14,200	13,000
Income tax holiday per diluted share (in dollars per share)				$ 0.17
Interest expense				$ 1,600	1,300	1,500
Decrease due to a lapse in the statute of limitations					600	300
Interest accrued				8,800	7,200
Unrecognized tax benefits		18,259		17,437	16,721	$ 18,259
Canada Revenue Agency
Income Tax Contingency
Potential tax charges				3,000
China
Income Tax Contingency
Tax holidays				4,100
Foreign Tax Authority
Income Tax Contingency
Deferred tax liabilities recognized on foreign earnings				13,900	12,600
Domestic Tax Authority
Income Tax Contingency
Deferred tax liabilities recognized on foreign earnings				$ 300	$ 400
Toll Charge
Income Tax Contingency
TCJA one-time charge		2,300
Toll Charge | IXYS Corporation
Income Tax Contingency
TCJA one-time charge	$ 7,000	7,000	$ (2,000)
Other Items
Income Tax Contingency
TCJA one-time charge		$ 900